Quoting Evan Bacon
Do you use Autodesk and Legolizer plugin
For this model we actually got our hands of a 3DS model, then imported it into BrickBuilder, which is a priopetary software that Lego developed for the design and construction of large sculptures such as this one.
Another Lego designer has posted on Youtube the video of how Lego Models are designed and built using this software.
Check out this link.